This invention pretains to gripper arm structures, and particularly to gripper arms suitable for use with insertion machines and the like.
Gripper arms have long been used with insertion machines of the type depicted in U.S. Pat. No. 2,325,455 to A. H. Williams which is commonly assigned herewith and incorporated herein by reference. Prior art gripper arms typically each have fixed and movable jaw members. The fixed jaw member is usually integral with the gripper arm while the movable jaw is selectively operated so that articles, such as documents or inserts, can be engaged between and released from the two jaws.
Prior art gripper arms have traditionally been mounted on two elongated shafts which extend above and along an insert track. The first or upper shaft, which oscillates once per machine cycle, has an upper portion of the gripper arm keyed thereto so that the gripper arm oscillates toward and away from a corresponding insertion supply station in timed relationship with the other operations occuring at the station. The second shaft also oscillates once during each machine cycle to actuate the movable jaw member into and out of engagement with the fixed jaw member in timed relationship with the oscillation of the gripper arm about the first shaft and with the rest of the machine. A cam keyed to the second shaft acts upon a connecting rod which in turn moves the movable jaw member away from the fixed jaw member against the action of a tension spring. The jaws are held apart in this manner until the gripper arm is oscillated toward the corresponding insertion station whereat the movable jaw is positioned above and the fixed jaw is positioned below an insert. The second shaft then oscillates to close the movable jaw against the fixed jaw to engage and grip the insert. The first shaft thereupon swings away from the insert station, pulling the selected insert therefrom in a direction toward the insert track. Over the insert track the second shaft is oscillated to move the movable jaw member away from the fixed jaw and thereby release the insert, permitting the insert to fall onto the table of the insertion transporting mechanism.
Although only one gripper arm structure has been described above, a plurality of such gripper arms are provided with an insertion machine, each gripper arm being positioned in relation to corresponding insert stations linearly arranged along an insert track. The area above the insert track is rather dense with mechanical parts including the two shafts which run through each gripper arm, as well as the associated cams and connecting rods for each gripper arm. It is a cumbersome operation to remove or replace an individual gripper arm since the arm must be removed from two shafts, each of which run the entire length of the insert track. Moreover, delicate mechanical adjustments are required for each gripper arm so that the movable jaw member associated therewith can be opened properly by gradual cam action taking into consideration the thickness of the insert materials in the hopper of the corresponding insert station.
Insertion machines of the type described above can operate through a range of speeds. An operator may at a lower end of the operational speed range "step" or "jog" the machine through a machine cycle at a very slow speed as is useful in the case of setting up the machine with new material. At high operational speeds the insertion machine may operate at a rate in the neighborhood of 10,000 cycles per hour.
In setting up an insertion machine, the operator must be cognizant of the fact that each insert must be released at a precise location along the insert track, usually within 1/8 inch of a specified precise location. The time delay associated with the actuation of the movable jaw member thus becomes a factor in determining where on the insert track the insert will be released. If the delay time in actuating the movable jaw member is constant regardless of the operational speed of the machine, significant error can occur in placement of the insert on the insert track. For example, a delay of 20 to 25 milliseconds in actuating the movable jaw member when the insertion machine is operating at 10,000 cycles per hour results in the gripper arm travelling approximately one inch. Thus, a given magnitude of time delay in actuating the movable jaw member in the jog mode or at low speed is not suitable for higher operational speeds and can, when the machine is operated at higher speeds, result in significant misplacement of the insert on the insert track.
In view of the foregoing, it is an object of the present invention to provide a gripper arm wherein the magnitude of delay involved in actuating a movable jaw member is related to the operational speed of the insertion machine in conjunction with which the gripper arm is employed.
An advantage of the present invention is the provision of a gripper arm having a movable jaw member capable of engaging articles regardless of the thickness of the articles.
Another advantage of the present invention is the provision of a gripper arm which is easily manufactured, installed, and removed for serviceability reasons.
Yet another advantage of the present invention is the provision of a gripper arm which has few moving parts, low mass, few lubrication points, and few points of friction and wear.
A further advantage of the present invention is the provision of a gripper arm wherein the coefficient of friction between an insert and a jaw member is increased, thereby increasing the force available to pull an insert from a hopper of a corresponding insert station but with less strain on the gripper arm.
Still another advantage of the present invention is the provision of a gripper arm having a movable jaw member which tightly grips inserts regardless of insert thickness.
Yet another advantage of the present invention is the provision of a gripper arm which, when installed in an insertion machine, facilitates easy access to and around an insert track of the insertion machine.